Are the anti-allergic properties of H-1-antihistamines of any clinical relevance?

Histamine is an ubiquitous messenger molecule synthetized and released fr-u rn human basophils, mast cells and neurons. Its various biological effects are mediated by three pharmacologically defined receptors termed the H-1, H -2 and H-3-receptors. The H-1-receptor was the first member of this family to be pharmacologically defined with the advent of selective antagonists. t he much less than antihistamines much greater than which are widely used to treat allergic disorders. Recent evidence indicates that cer lain antihist amines exert antiallergic effects nor related to H-1-antagonism. However, t hese effects require higher doses than those regularly used. We have demons trated thar histamine induces a concentration-dependent release of IL-G, TN F-alpha and beta-glucuronidase from human lung macrophages. These effects a re inhibited by fexofenadine. an H-1-receptor antagonist, but not by cimeti dine, an H-2-receptor antagonist. The finding that fexofenadine inhibits th e human lung macrophages-activating property of histamine raises the possib ility that long-ter-m treatment with fexofenadine might inhibit tissue dama ge caused by human lung macrophages activated hy histamine immunologically released by basophils and mast cells.